Slides from a recent presentation on the new functional core of 2.0:
http://www.digitalmars.com/d/2.0/accu-functional.pdf
They basically add "invariant" and "const" qualifiers to types, and a
"pure" qualifier for functions, which ensures functional purity of those
functions.
The type system has the flavour of many of the requirements object
capabilities impose on a language: invariant and const qualifiers apply
transitively to all nested types, and they establish various safe
implicit conversions.
Not fully object-capability, but getting closer.
Sandro